Technical Field
The present disclosure generally relates to techniques for mounting a component onto a substrate, and in particular, to bonding a camera lens assembly to a substrate for use in a mobile electronic device.
Description of the Related Art
Attaching components to a substrate inside a microelectronic device such as a camera module for a smart phone becomes more and more difficult as devices become smaller and substrate real estate becomes more constrained. Component attachment is typically accomplished by dispensing glue onto the substrate, and using a pick-and-place robot to lift up a component and set it down at a prescribed location on the substrate. To attach a hollow component such as a camera lens assembly, glue is dispensed in line patterns and the component is attached in such a way that the perimeter of the component coincides with the glue line. One problem that arises in mounting components is that the epoxy used to bond the components to the substrate can bleed onto neighboring contact pads or bond pads, thereby interrupting electrical connections or interfering with next process steps. Even if the epoxy is dispensed in narrow glue lines, when the component is pressed into the epoxy, the foot of the component displaces some of the glue, which then flows onto the neighboring contact pads. One way to decrease the amount of glue displaced is to narrow the glue line further. However, switching to a new epoxy formula may be necessary in order to achieve a comparable joint with less glue volume. Qualifying a new type of epoxy for introduction into a manufacturing process can be a very complex, time-consuming, and costly process. Another method of bonding involves dispensing epoxy onto the substrate in a narrow glue line that corresponds to only a partial perimeter of the component wall. The rest of the perimeter will simply not receive any glue. When the component is then aligned with the narrow glue line, applying pressure along the partial perimeter that has glue underneath it will displace some of the glue, but the remaining component perimeter will just sit on top of the substrate. After curing the epoxy, a rigid joint will form in the usual way along the partial perimeter. Bonding using such a method can solve the glue displacement problem by designing the substrate layout so that particularly vulnerable areas of the substrate are near the unglued portion of the perimeter.
However, there are potential drawbacks to such a method of partial gluing. First, the unglued portion of the component may not be completely stationary and it may rub against the substrate. In some applications such friction may not matter. In other applications, such friction may generate an unacceptable number of particles, or the component may not be bonded tightly enough. In addition, in the case of camera components, light leakage at the location of the unglued portion may affect the optical performance of the camera. Furthermore, debris may pass underneath the unglued portion of the mount wall and collect underneath the component. In addition, a broken glue line is more likely to separate from the substrate than is a continuous glue line.